When I got my hands on a Haswell based Ultrabook, Acer's recently announced S7, I was somewhat disappointed to learn that Acer had chosen to integrate Intel's HD 4400 (Haswell GT2) instead of the full blown HD 5000 (Haswell GT3) option. I published some performance data comparing HD 4400 to the previous generation HD 4000 (Ivy Bridge GT2) but added that at some point I'd like to take a look at HD 5000 to see how much more performance that gets you. It turns out that all of Apple's 2013 MacBook Air lineup features Haswell GT3 (via the standard Core i5-4250U or the optional Core i7-4650U). Earlier today I published our review of the 2013 MBA, but for those not interested in the MBA but curious about how Haswell GT3 stacks up in a very thermally limited configuration I thought I'd do a separate post breaking out the findings.

In mobile, Haswell is presently available in five different graphics configurations:

Intel 4th Generation Core (Haswell) Mobile GPU Configurations

Intel Iris Pro 5200

Intel Iris 5100

Intel HD 5000

Intel HD 4400

Intel HD 4200

Codename

GT3e

GT3

GT3

GT2

GT2

EUs

40

40

40

20

20

Max Frequency

1.3GHz

1.2GHz

1.1GHz

1.1GHz

850MHz

eDRAM

128MB

-

-

-

-

TDP

47W/55W

28W

15W

15W

15W

The top three configurations use a GPU with 40 EUs, while the HD 4400/4200 features half that. Intel will eventually introduce Haswell SKUs with vanilla Intel HD Graphics, which will only feature 10 EUs. We know how the Iris Pro 5200 performs, but that's with a bunch of eDRAM and a very high TDP. Iris 5100 is likely going to be used in Apple's 13-inch MacBook Pro with Retina Display as well as ASUS' Zenbook Infinity, neither of which are out yet. The third GT3 configuration operates under less than a third of the TDP of Iris Pro 5200. With such low thermal limits, just how fast can this GPU actually be?

Compared to Intel's HD 4000 (Ivy Bridge/dark blue bar), Intel claimed roughly a 25% increase in performance with HD 5000 in 3DMark06 and a 50% increase in performance in 3DMark11. We now have the systems to validate Intel's claims, so how did they do?

In 3DMark 11 we're showing a 64% increase in performance if we compare Intel's HD 5000 (15W) to Intel's HD 4000 (17W). The 3DMark06 comparison yields a 21% increase in performance compared to Ivy Bridge ULV. In both cases we've basically validated Intel's claims. But neither of these benchmarks tell us much about actual 3D gaming performance. In our 2013 MBA review we ran a total of eight 3D games. I've summarized the performance advantages in the table below:

The data ranges from a meager 2.3% advantage over Ivy Bridge ULV to as much as 40.8%. On average, Intel's HD 5000 offered a 15.3% performance advantage over Intel's HD 4000 graphics. Whether or not that's impressive really depends on your perspective. Given the sheer increase in transistor count, a 15% gain on average seems a bit underwhelming. To understand why, you have to keep in mind that the performance gains come on the same 22nm node, with a lower overall TDP. Haswell ULT GT3 has to be faster, with less thermal headroom than Ivy Bridge ULV GT2.

The range of performance improvement really depends on turbo residency. With only a 15W TDP (inclusive of the CPU and PCH), games that have more CPU activity or the right combination of GPU activity will see lower GPU clocks. In Borderlands 2 for example, I confirmed that the GT3 GPU alone was using up all of the package TDP thus forcing lower clocks:

All of this just brings us to the conclusion that increasing processor graphics performance in thermally limited conditions is very tough, particularly without a process shrink. The fact that Intel even spent as many transistors as it did just to improve GPU performance tells us a lot about Intel's thinking these days. Given how thermally limited Haswell GT3 is at 15W, it seems like Broadwell can't come soon enough for another set of big gains in GPU performance.

I also put together a little graph showing the progression of low TDP Intel GPU performance since Sandy Bridge. I used GRID 2 as it seemed to scale the most reasonably across all GPUs:

Note how the single largest gain happens with the move from 32nm to 22nm (there was also a big architectural improvement with HD 4000 so it's not all process). There's definite tapering that happens as the last three GPUs are on 22nm. The move to 14nm should help the performance curve keep its enthusiasm.